The causes of the most common type of high blood pressure, essential hypertension, probably begin in childhood in the family setting. With increasing age, the prevalence of hypertension increases. The actual level of blood pressure in adults has been shown to be one of the strongest predictors of future level of blood pressure. Tracking of blood pressure has also been demonstrated in children--that is, persons with high normal blood pressure continue over time to have high blood pressure. After screening of 10,447 elementary school children, 79 families of children in the top 5% of the systolic blood pressure distribution were randomized to a control group (39) whose blood pressures and height and weight are monitored annually and an intervention group (40) whose sodium consumption is reduced by continuous reinforcement of behavior modification. Blood pressures of the children in these families are measured twice per year in the schools by a separate group of technicians. Additionally, a stratified random sample of 1,793 children over the whole range of blood pressure distributions are continuing to be screened at school twice yearly. The families of those children have undergone extensive medical and psychological tests and completed nutritional questionnaires and given urine specimens for sodium and potassium analysis. Contrasts will be made between ethnic groups and those families in the high and low levels of blood pressure distribution.